Association-dissociation reactions

Enzyme inhibitors are classified in several ways. The inhibitor may interact either reversibly or irreversibly with the enzyme. Reversible inhibitors interact with the enzyme through noncovalent association/dissociation reactions. In contrast, irreversible inhibitors usually cause stable, covalent alterations in the enzyme. That is, the consequence of irreversible inhibition is a decrease in the concentration of active enzyme. The kinetics observed are consistent with this interpretation, as we shall see later. 

Just as in the case of (16), an equation of the form (20) applies to any other association-dissociation reaction in which one of the dissociated species is mobile, the other fixed. When the two species are distinct but both mobile, as for hydrogen combining with, say, an interstitial silicon, a similar line of reasoning, whose details we omit, leads to equations of the same form as (16) and (20) but with D+ replaced by the sum of the diffusion coefficients of the two species. When the two mobile species are the same, as for the reaction H° + H° 5H2, it turns out that nA and n+ should each be replaced by the monatomic density n, D+ by the monatomic diffusion coefficient, and 4ir by 8tt in (16) but not in (20). 

A quantitative discrimination between labile and nonlabile complexes is made by comparing the diffusion timescale with those of the association/dissociation reactions (or alternatively, the reaction layer, /i (equation (58)) and the diffusion layer, <5, thicknesses (e.g. equations (15), (18) and (19)). 

Furthermore, although the rates of addition and loss may differ at each end (i.e., the transition states for the individual association-dissociation reactions may depend on the polarity of protomer-polymer interactions), the initial state (protomer + MT ) and the final state (MT +i) are independent of the pathway for protomer addition. This result is true because addition or loss of a protomer at either end leads to structurally indistinguishable polymers. Thus, the energetics of the reactions at each end are the same, and Ki equals for the case of no nucleotide hydrolysis accompanying assembly. We may then reexpress the rate equations for protomer addition or loss to the two ends in the following manner ... 

It is well known that the association-dissociation reaction goes in both directions and that there is always some finite fraction of ion pairs [28]. Counter ions that form ion pairs do not participate in creating osmotic pressure accounting for such counter ions is thus important for the correct determination of the dimensions of the network. 

The extension of matrix IET to bulk reversible association-dissociation reactions [282] and reversible excitation binding [283]... 

Although B-lactoglobulin and a-lactalbumin are capable of the above association/dissociation reactions, they probably have little importance in determining functional properties in food applications in the pH 6 to 7 range. However, protein concentration, pH and other related factors do affect their susceptibility to heat denaturation (17). 

The major soy proteins, the 7S and the 11S globulins are characterized by complex quaternary structures easily undergoing association-dissociation reactions. Salt has a unique stabilizing effect on the quaternary structure of both the 7S and the 11S globulins, which influences most physical properties of soy proteins. 

It is usually assumed that the association-dissociation reactions occur at the membrane interfaces. Selectivity of this facilitated transfer is based on the different affinity of the carrier for the components of the source phase. In artificial liquid membrane systems, crown ethers are widely used as carriers to separate metal ions. Most of the ethers are photoresponsive and their structure and resulting metal-binding ability can be altered under irradiation. 

For low-molecular weak electrolytes the concentration dependence of conductance is more complex, as in addition to the interionic friction effect it is strongly influenced by the association-dissociation reactions taking place in the solutions. However, as these in general follow the mass action law and thus, in simpler cases, the van t Hoff dilution law, their conductivity behavior is predictable. As a rule their equivalent conductivity steeply increases on dilution due to the increased dissociation of the electrolyte. 

Popov, A.V., Agmon, N., Gopich, TV, Szabo, A. Influence of diffusion on the kinetics of excited-state association-dissociation reactions Comparison of theory and simulation. J. Chem. Phys. 2004, 120, 6111. 

Experimental experience demonstrates that in any case large reaction dipole moments AM) are required to produce major displacements of dipolar equilibria high ionic valencies are necessary for larger dissociation field effects in ionic association-dissociation reactions/ ... 

We use the hydrolysis of A into P and Q as an illustration. Examples are the hydrolysis of benzylpenicillin (pen G) or the enantioselective hydrolysis of L-acetyl amino acids in a DL-mixture, which yields an enantiomerically pure L-amino acid as well as the unhydrolysed D-acetyl amino acid. In concentrated solutions these hydrolysis reactions are incomplete due to the reaction equilibrium. It is evident that for an accurate analysis of weak electrolyte systems, the association-dissociation reactions and the related phase behaviour of the reacting species must be accounted for precisely in the model [42,43]. We have simplified this example to neutral species A, P and Q. The distribution coefficients are Kq = 0.5 and Kp = K = 2. The equilibrium constant for the reaction K =XpXQ/Xj = 0.01, where X is a measure for concentration (mass or mole fractions) compatible with the partition coefficients. The mole fraction of A in the feed (z ) was 0.1, which corresponds to a very high aqueous feed concentration of approximately 5 M. We have simulated the hydrolysis conversion in the fractionating reactor with 50-100 equilibrium stages. A further increase in the number of stages did not improve the conversion or selectivity to a significant extent. Depending on the initial estimate, the calculation requires typically less than five iterations. 

Hence, during this stage transport by the association-dissociation reaction and by migration of complexes is also to be expected. Another effect connected with vacancy behavior, which influences the effective activation energy for migration and hence the ordering rate, will be considered below. 

Under time-dependent chain deformation and orientation of the chain segments, the angular distribution of the rate of production of clusters f3g at any instant of time t by the association-dissociation reaction reads... 

An example of direct measurements based on the frequency representation of fluctuation is the study of the association-dissociation reaction of BeS04 in a 0.03 M solution, with conductance measurements (Feher Weismann, 1973). It is particularly interesting that they could increase the ratio of the reaction noise to Johnson noise of the circuit, since the former is a quadratic function of the applied direct voltage, while the latter is independent of the voltage. 

Consider the equilibrium constant of the homonuclear association-dissociation reaction... 

Inoue et al. also derived an expression of %2 by using the stepwise association/dissociation reactions (4), including the counterions and assuming all reaction steps to be fast except an intermediate step that is slow and rate-limiting. 

For the association-dissociation reaction Eq. [1], the equilibrium constant is given approximately as" ... 

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